Metakaolin is a very useful aluminosilicate material that has high value applications. For example, there is usage in various applications of the cement industry as found say with U.S. Pat. No. 6,230,804 and U.S. Pat. No. 5,158,613. With lower costs inherent in a new and simple metakaolin production process, the use of metakaolin could significantly increase, particularly in the cement industry, as high performance concretes formed with added metakaolin, are significantly stronger and more economically attractive.
The current method of producing metakaolin involves two distinct stages whereby high grade kaolin is first produced from kaolin ore in a multiple step procedure. The high grade kaolin is then heated in a high temperature furnace at about 500-900° C. to produce metakaolin. This is outlined in “Effect of Metakaolin on Durability of Concrete Structures and Bridges, V. H. Nejad, Univ. of Surrey, UK, 1995”. With calcinations of kaolin, care must be taken to complete the dehydroxylation of kaolin, but prevent heating beyond this point since this leads to the formulation of unreactive mullite, 3A12.2SiO2.
The production of high grade kaolin contains a number of steps and these lead to complex and expensive processes to obtain good quality kaolin necessary as a feedstock to produce metakaolin. The complexity is amply illustrated in the art taught in U.S. Pat. No. 6,186,335 (February, 2001) by Arrington-Webb et al. The inventors of this art have indicated that in excess of six steps could be required to produce good quality kaolin product from kaolin ore. The complexity of the overall process is a major factor in high capital and operating costs and high kaolin costs leading to expensive metakaolin.
There is also significant additional art on record to support the view that using high quality kaolin for metakaolin production is complex and costly. This is particularly true as the higher grade kaolin ore reserves have been depleted leaving primarily lower grade, high impurity, kaolin reserves left as kaolin feedstock. References related to this include as examples, U.S. Pat. Nos. 5,891,326; 5,545,599; 5,227,349; 5,047,375 and 4,492,628.
The result of the complex process for producing metakaolin is that the use of metakaolin is quite limited by the high costs associated with current methods of production. In addition, many highly beneficial potential uses of metakaolin, such as high strength and high performance concretes, are not pursued due to high costs of metakaolin.
What is needed is a new and low cost process route for the manufacture of metakaolin so that new and economical formulations of metakaolin, with alternate concrete formulations, can be manufactured and sold at much better pricing to significantly expand market use through superior materials performance.